Thermal printing head

ABSTRACT

A thermal printhead includes plural groups of drive ICs (DrIC 1-14 ), a plurality of main conductor wirings ( 31-34 ) for transmitting signals to the drive ICs in the respective groups, and a plurality of auxiliary conductor wirings ( 41-43 ) respectively provided to accompany the main conductor wirings for providing conduction between the drive ICs in adjacent groups. The main conductor wirings and the auxiliary conductor wirings respectively include severable sites (a-f) for severing electrical conduction of the main conductor wirings and the auxiliary conductor wirings. A plurality of recovery wiring portions ( 32   a   -34   a  and  41   a   -43   a ) are provided to the respective severable sites in parallel thereto. Each of the recovery wiring portions includes a pair of pads spaced from each other.

TECHNICAL FIELD

The present invention relates to a thermal printhead for forming imageson thermosensitive paper or on recording paper via a thermal-transferink ribbon.

BACKGROUND ART

As is well known, thermal printheads are used for forming intendedimages by selectively providing thermal energy to thermosensitive paperor a thermal-transfer ink ribbon. Generally, thermal printheads aredivided mainly into thin film-type thermal printheads and thickfilm-type thermal printheads depending on methods of forming theirheating resistors. As an example, a typical thick film-type thermalprinthead will be described below.

FIG. 1 shows a conventionally used thick film-type thermal printhead 1.As will be described later, a thermal printhead according to the presentinvention has a structure similar to that shown in FIG. 1 except for itscharacteristic portions.

The thermal printhead 1 shown in FIG. 1 includes a head substrate 11formed of alumina ceramic and an additional substrate 20 formed ofglass-fiber-reinforced epoxy resin. The head substrate 11 is providedwith a linear heating resistor 12, a plurality of drive ICs 13, a commonelectrode 14 and a plurality of individual electrodes 15. The heatingresistor 12 extends longitudinally of the head substrate. The drive ICs13 are arranged in a row extending in the longitudinal direction of thehead substrate.

The common electrode 14 is integrally formed with a plurality ofcomb-teeth like projections 16 extending parallel to each other. Eachprojection 16 has a free end electrically connected to the heatingresistor 12. Each individual electrode 15 is linear and has two freeends. As shown in FIG. 1, the individual electrodes 15 and the pluralityof projections 16 are alternately disposed. One free end of eachindividual electrode 15 is positioned between two adjacent projections16 of the common electrode 14 to be electrically connected to theheating resistor 12, whereas the other free end is connected, via aconductive wire 19, to an output pad (not shown) of a relevant drive IC13. With such an arrangement, the heating resistor 12 includes aplurality of regions 18 each defined between two adjacent projections16. These regions function as heating dots under the control of thedrive ICs 13. Specifically, a current is supplied to the region 18selected by the drive ICs 13 via the adjacent projection 16 and theindividual electrode 15. As a result, the selected region is heated upto function as a heating dot.

The additional substrate 20 is formed with a wiring pattern (partiallyshown) which is connected to input pads (not shown) of the drive ICs 13via a plurality of conductive wires 19 a. The additional substrate 20 isfurther provided with a connector 17 connected to the wiring pattern.The connector 17 is also connected to a cable (not shown) fortransmitting signals supplied from outside. With the above arrangement,the external signals are transmitted via the wiring pattern to the driveICs 13. The drive ICs 13 will operate based on the thus transmittedsignals.

Each of the drive ICs 13 incorporates a shift register which has apredetermined number of bits corresponding to the number of the outputpads of the drive IC 13. The drive ICs 13 have their data-out terminalsconnected in cascade to their data-interminals, so that the shiftregisters in the respective drive ICs 13 are connected to each other.

The thermal printhead having the above structure operates as follows. Inorder to perform printing for one line, printing data for the line needbe input to the drive ICs 13 in advance. To this end, the printing datafor the line are serially fed to the leftmost drive IC 13 shown in FIG.1 via the data-in terminal. Then, the printing data are successively fedto the shift registers of the respective drive ICs 13 connected incascade to each other, and retained in them. In accordance with theretained printing data, the output pads of the drive ICs 13 areselectively actuated in synchronism with a strobe signal fed to eachdrive IC 13. As a result, the heating dots 18 are selectively heated upfor performing a predetermined printing operation.

Unfavorably, the thermal printhead 1 having the above arrangement hasthe following problems. Since the printing data for one line areserially fed to the drive ICs 13, the printing operation for the linecannot be started until the input of the serial data is completed. Thismeans that, in the above thermal printhead, it is impossible to improvethe printing speed beyond a certain limit due to the serial data input.Further, when all the heating dots 18 are actuated simultaneously, anincreased amount of current will pass through the common electrode 14.Consequently, the voltage drop along the common electrode 14 isintensified, which leads to uneven printing results.

To deal with the above problems, the following measures haveconventionally been taken. To begin with, printing data for one line aredivided into a predetermined number of pieces, while the drive ICs 13are also divided into the same number of groups. Then, each piece of thedivided printing data is simultaneously fed to a corresponding one ofthe groups of the drive ICs 13. Compared with the serial input describedabove, this method is advantageous in that the printing data can be fedto the drive ICs 13 more quickly, so that the printing speed isimproved. In addition, by staggering the timing of driving therespective groups of drive ICs 13, the current flowing through thecommon electrode 14 will be decreased, thereby reducing the voltage dropalong the common electrode 14.

However, the above method suffers the following problem. To feed thedivided data to the respective groups of drive ICs 13, a special wiringpattern designed for that particular purpose is needed. Therefore, it isnecessary to prepare different kinds of wiring patterns, such as awiring pattern suitable for the use of two-grouped printing data or awiring pattern suitable for the use of three-grouped printing data,depending on the characteristics of a device in which the thermalprinthead 1 is incorporated or on the need of a user. To individuallymanufacture such thermal printheads having different kinds of wiringpatterns requires additional time and trouble, thereby leading to anincrease in cost. Further, in order to actuate the drive ICs 13 group bygroup with time difference, a wiring pattern for supplying strobesignals needs to be additionally designed in accordance with theparticular divisional manner.

Moreover, the design of the various wiring patterns mentioned above mayneed to be altered after they are produced. For instance, a user maywish to use a wiring pattern designed for three-grouped printing data inplace of the originally used wiring pattern designed for two-groupedprinting data. Conventionally, in such a situation, a thermal printheadincorporating a wiring pattern designed for three-grouped printing datamay need to be purchased additionally, which is very inconvenient.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide a thermalprinthead which is capable of solving the above problems.

In accordance with the present invention, there is provided a thermalprinthead comprising:

drive ICs divided into a plurality of groups;

a plurality of main conductor wirings for transmitting signals to therespective groups of the drive ICs; and

a plurality of auxiliary conductor wirings arranged to accompany themain conductor wirings, respectively, for connecting the drive ICs inadjacent groups;

wherein each main conductor wiring and each auxiliary conductor wiringinclude a severable site for severing electrical conduction of said eachmain conductor wiring and said each auxiliary conductor wiring.

In the thermal printhead having the above arrangement, a selected one ofthe severable site of said each main conductor wiring and the severablesite of the auxiliary conductor wiring accompanying said each mainconductor wiring may be severed.

Further, all the severable sites of the main conductor wirings maybesevered. Still further, all the severable sites of the auxiliaryconductor wirings may be severed.

Each of the severable sites may be formed with a marking.

Preferably, the thermal printhead may further comprise a plurality ofrecovery wiring portions arranged in parallel to the severable sites,respectively. Each recovery wiring portion may include a pair of padsspaced from each other.

Various features and advantages of the present invention will becomeclearer from the description given below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing arrangements of a thermal printhead whichare common to the prior art and the present invention.

FIG. 2 is a sectional view showing the same thermal printhead.

FIG. 3 is a schematic view showing a wiring pattern for the printingdata according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As previously described, a thermal printhead according to the presentinvention has a structure substantially the same as that of theconventional thermal printhead shown in FIG. 1. Therefore, the thermalprinthead according to the present invention will also be described withreference to FIG. 1 (and other figures).

Specifically, the thermal printhead 1 according to the present inventionincludes a head substrate 11 formed of e.g., alumina ceramic, and anadditional substrate 20 formed of e.g., glass-fiber-reinforced epoxyresin. The head substrate 11 is provided with a linear heating resistor12, a plurality of drive ICs 13, a common electrode 14 and a pluralityof individual electrodes 15. The heating resistor 12 extendslongitudinally of the head substrate. The drive ICs 13 are linearlydisposed in the longitudinal direction of the head substrate.

The common electrode 14 is integrally formed with a plurality ofcomb-teeth like projections 16 extending parallel to each other. Eachprojection 16 has a free end electrically connected to the heatingresistor 12. Each individual electrode 15 has an elongated configurationand has two free ends. As shown in FIG. 1, the individual electrodes 15and the plurality of projections 16 are alternately disposed. One freeend of each individual electrode 15 is positioned between two adjacentprojections 16 of the common electrode 14 to be electrically connectedto the heating resistor 12. On the other hand, the other free end of theindividual electrode 15 is connected, via a conductive wire 19 such as agold wire, to an output pad (not shown) of a relevant drive IC 13. Eachof the drive ICs 13 is provided with power and signal pads (not shown).Further each drive IC 13 incorporates a shift register. The shiftregister has a predetermined number of bits corresponding in number tothe output pads of the drive IC 13.

With the above arrangement, the heating resistor 12 includes a pluralityof regions 18 (See FIG. 1) each of which is defined by adjacentprojections 16. The respective regions operate as heating dots undercontrol of the drive ICs 13. More specifically, a current is supplied tothe region 18 selected by the drive ICs 13, via the adjacent projection16 and the individual electrode 15. As a result, the particular regionis heated up to function as a heating dot.

The additional substrate 20 carries a connector 17. This connector 17 isarranged to be connected to a cable (not shown) which is used fortransmitting signals supplied from outside. The additional substrate 20is further formed with a wiring pattern which is connected to e.g., thesignal pads of the drive ICs 13 via wires 19 a.

As shown in FIG. 2, the drive IC 13, the bonding wires 19, 19 a arecovered with a protective coating 25 formed of e.g., a hard coatingmaterial.

The most significant feature of the present invention is the wiringpattern formed on the head substrate 20. This wiring pattern will bedescribed below with reference to FIG. 3.

The illustrated wiring pattern is designed so that printing data for oneline supplied via the connector 17 are transmitted to the drive ICs 13in a manner which permits the printing data to be divided in to amaximum of four groups. Specifically, the fourteen drive ICs 13 aredivided into four groups. The first group includes four drive ICs(DrIC1-4), the second group three drive ICs (DrIC5-7), the third groupfour drive ICs (DrIC8-11), and the fourth group three drive ICs(DrIC12-14). In each group, the drive ICs are electrically connected toeach other.

The illustrated wiring pattern includes four main conductor wirings31-34 and three auxiliary conductor wirings 41-43. One ends of therespective main conductor wirings 31-34 are connected to the connector17. The other ends of the main conductor wirings 31-34 are connected,respectively, to the data-in pad (DI) of the drive IC (DrIC1), thedata-in pad (DI) of the drive IC (DrIC5), the data-in pad (DI) of thedrive IC (DrIC8), and the data-in pad (DI) of the drive IC (DrIC12). Thethree auxiliary conductor wirings 41-43 are arranged to connect,respectively, the data-out pad (DO) of the drive IC (DrIC4) to thedata-in pad (DI) of the drive IC (DrIC5), the data-out pad (DO) of thedrive IC (DrIC7) to the data-in pad (DI) of the drive IC (DrIC8), andthe data-out pad (DO) of the drive IC (DrIC11) to the data-in pad (DI)of the drive IC (DrIC12).

The main conductor wirings 32-34 are provided with severable sites d-frespectively for severing electrical conduction of the main conductorwirings. The severable sites may be provided with predetermined markingsfor facilitating visual recognition. Similarly, the auxiliary conductorwirings 41-43 are provided with severable sites a-c respectively forsevering electrical conduction of the auxiliary conductor wirings. Theseverable sites may also be provided with predetermined markings.

Further, the main conductor wirings 32-34 are provided with recoverywiring portions 32 a-34 a, respectively, each of which extends so as tobridge a corresponding one of the severable sites d-f. Each of therecovery wiring portions includes two spaced pads and conductor wiringsfor connecting the respective pads to the main conductor wiring.Similarly, the auxiliary conductor wirings 41-43 are provided withrecovery wiring portions 41 a-43 a, respectively, each of which extendsto bridge a corresponding one of the severable sites a-c. Each of therecovery wiring portions includes two spaced pads and conductor wiringsfor connecting the respective pads to the auxiliary conductor wiring.Each severable site may be bypassed by connecting the two spaced pads ofthe recovery wiring portion by soldering or wire-bonding.

The wiring pattern thus formed may be utilized as follows. It should benoted that, in the description given below, all the severable portionsa-f are depicted as being connected in the initial state.

It is now supposed that the one-line printing data divided into fourgroups are to be supplied to the drive ICs. In this case, the severableportions a, b and c shown in FIG. 3 will be severed by etching or NCmachining for example. In this manner, a piece of printing data suppliedthrough the main conductor wiring 31 is transmitted from the leftmostdrive IC (DrIC1) to the rightmost drive IC (DrIC4) of the first group.Similarly, a piece of printing data supplied through the main conductorwiring 32 is transmitted from the leftmost drive IC (DrIC5) to therightmost drive IC (DrIC7) of the second group, a piece of printing datasupplied through the main conductor wiring 33 is transmitted from theleftmost drive IC (DrIC8) to the rightmost drive IC (DrIC11) of thethird group, and a piece of printing data supplied through the mainconductor wiring 34 is transmitted from the leftmost drive IC (DrIC12)to the rightmost drive IC (DrIC14) of the fourth group.

Now, it is supposed that the one-line printing data are to be dividedinto two groups for supply to the drive ICs. In this case, the severableportions b, d and f are severed, as may easily be understood.Alternatively, when the whole one-line printing data are seriallytransmitted in one group, the severable portions d, e and f are severed.

Once the severable portions a, b and c have been severed for enablingfour-group transmission of the printing data, the wiring pattern can bealtered into the two division form in the following manner. First, theseverable portions d and f are severed. Then, the recovery wiringportions 41 a, 43 a are electrically connected. As a result, the wiringpattern is modified so that the one-line printing data divided into twogroups will be transmitted to the drive ICs.

In the thermal printhead 1 of the present invention, as is clear fromthe above, a single wiring pattern can be modified to a selected one ofthe one-division, two-division and four-division patterns, as required,in the above-described manner. Thus, it is possible to provide variouskinds of divisional patterns without individually preparing the wiringpatterns corresponding to the respective divisions. Therefore, in thethermal printhead 1 formed with the wiring pattern described above, bysevering the main conductor wiring or the auxiliary conductor wiring,the drive ICs may be divided into a desired number of groups inaccordance with the order from a user for example. Thus, the time andtrouble taken for designing can be reduced.

Further, when the main conductor wiring and the auxiliary conductorwiring are to be severed by using a NC machining technique, it sufficesto prepare a new program for controlling the movement of the processinghead of the device performing the NC machining. This requires less timeand trouble than the additional designing of a plurality of wiringpatterns.

Further, as described above, it is possible to reconnect the oncesevered auxiliary conductor wirings 41, 42, 43 by connecting therecovery wiring portions 41 a, 42 b and 43 c. This means that thedivisional number once determined can be altered. It is clear that thesimilar operation can be performed with respect to the main conductorwirings 32-34 provided with the recovery wiring portions 32 a-34 a.

In the above embodiment, the drive ICs 13 are divided into four groups.However, it is obvious that the drive ICs 13 may be divided into anothernumber of groups.

Further, in the above embodiment, the main conductor wirings and theauxiliary conductor wirings are described as being initially connectedat the severable portions. Alternatively, all the severable portions maybe severed in the initial state. Even in this case, it is possible toachieve a desired number of division by connecting the spaced pads ofthe recovery wiring portions. It may also be possible to have only oneselected severable portion severed in the initial state.

In the above embodiment, the wiring pattern for transmitting printingdata is described. The present invention, however, may be applied to awiring pattern for transmitting clock signals, strobe signals, or strobeclock signals.

Further, in the above embodiment, the wiring pattern and the drive ICsare mounted on separate substrates 10 and 11, respectively. However, thewiring pattern and the drive ICs may be mounted on a common substrate.

The present invention is applied to a thick film-type thermal printheadin the above embodiment. However, the present invention may also beapplied to a thin film-type thermal printhead.

INDUSTRIAL APPLICABILITY

As described hereinbefore, the thermal printhead according to thepresent invention may advantageously be used based on one-line printingdata or the like which may be divided into plural pieces.

What is claimed is:
 1. A thermal printhead comprising: drive ICs dividedinto a plurality of groups; a plurality of main conductor wirings fortransmitting signals to the respective groups of the drive ICs; and aplurality of auxiliary conductor wirings arranged to accompany selectedones of the main conductor wirings, respectively, for connecting thedrive ICs in adjacent groups; wherein each selected main conductorwiring and the auxiliary conductor wiring accompanying said eachselected main conductor wiring are directly connected to each other,said each selected main conductor wiring and each auxiliary conductorwiring being formed with a severable site for severing electricalconduction of said each selected main conductor wiring and said eachauxiliary conductor wiring.
 2. The thermal printhead according to claim1, wherein a selected one of the severable site of said each selectedmain conductor wiring and the severable site of the auxiliary conductorwiring accompanying said each selected main conductor wiring is severed.3. The thermal printhead according to claim 1, wherein all the severablesites of the selected main conductor wirings are severed.
 4. The thermalprinthead according to claim 1, wherein all the severable site of theauxiliary conductor wirings are severed.
 5. The thermal printheadaccording to claim 1, wherein each of the severable sites is formed witha marking.
 6. The thermal printhead according to claim 1, furthercomprising a plurality of recovery wiring portions arranged in parallelto the severable sites, respectively.
 7. The thermal printhead accordingto claim 6, wherein each recovery wiring portion includes a pair of padsspaced from each other.